This invention relates to interconnection of electronic systems and, in particular, to the shielding of such interconnections.
In the prior art, communications switching systems such as circuit switching systems and data switching systems have a problem with the installation and subsequent need to increase capacity of small systems. For example, telecommunication switching system (circuit-switching) manufacturers face an economic hurdle to install a system that can handle twenty telephones but can grow to one hundred telephones. The initial system that is installed to handle twenty telephones is extremely cost-sensitive to the addition of such things as external connectors for the later attachment of cables for an additional system cabinet that will provide more telephones at a later point in time. The prior art has resolved this problem as illustrated in FIGS. 1-3. The initial system that is installed is switching system 101 which can handle a maximum number of telephones. Switching system 101 is mounted in a rack or a cabinet. When the capacity of switching system 101 has been exceeded, the architecture of switching system 101 allows printed circuit extender 103 to be plugged into the back plane of switching system 101 so as to extend the back plane. Printed circuit extender 103 then plugs into switching system 102 that will add the additional capacity to handle more telephones. Printed circuit extender 103 plugs directly into the back plane via a slot that would normally be utilized for a printed circuit board. Hence, switching system 101 does not have to have an external connector permanently wired to the printed circuit board that allows a cable to transfer the signals from the back plane to switching system 102. In addition, it is difficult to maintain the proper electrical characteristics when going from a back plane to a cable composed of wires without utilizing additional drivers that add greatly to the initial cost of the system. At present within the prior art, printed circuit extender 103 is simply positioned through opening 301 of FIG. 3 in switching system 101 and a similar opening in switching system 102. Since printed circuit extender 103 is a printed circuit board which is not adequately shielded against the radiation of electromagnetic interference (EMI), the portion of printed circuit extender 103 that is exposed as illustrated by distance 104 in FIG. 1 can radiate electromagnetic energy causing interference. In addition, EMI can also radiate from opening 301 from switching system 101 and similarly from switching system 102. Adding to this problem is the fact that distance 104 can vary due to mounting considerations in the field. Note, that whereas switching systems 101 and 102 are illustrated as being mounted side by side which is often the case for telecommunication systems, switching system 102 can be mounted on a rack directly below switching system 101 in a rack which is often the case for packet switching systems. Printed circuit extender 103 then would extend in the vertical direction.
To resolve these problems what is needed is a method of shielding printed circuit extender 103 utilizing an apparatus that is light and whose length is adjustable.
The foregoing problems are solved and a technical advance is achieved by an adjustable sleeve that provides electromagnetic interference (EMI) shielding, is lightweight, and is adjustable in its length. The electromagnetic compatibility sleeve is formed by attaching electromagnetic foil shields on one or both sides of an insulating material that is accordion-in-structure in a first embodiment so that its length is flexible. Advantageously, the insulating material can be a very high resistivity and magnetically lossy ferrite material to prevent eddy currents on the inner surface from causing magnetic fields within the insulating material. In a second embodiment, the sleeve is made up of telescoping sections so that the length is flexible. This flexible sleeve is attached to systems by the utilization of a mounting bracket, one for each system. Advantageously, the electromagnetic sleeve confines the radiation from a printed circuit extender to within the sleeve and prevents radiation from exiting the systems through enclosure openings by the utilization of the mounting brackets.
These and other features and advantages of the invention will become apparent from the following description of the illustrated embodiments of the invention considered together with the drawing.